In the construction of a heat exchanger, a large number of tubes must pass through a tube sheet, and leak-proof joints must be formed between the tubes and the sheet. When the heat exchanger is to be used as a part of a nuclear power plant, unusually high standards of reliability are called for since the tube sheet, which is made of steel as much as two-feet thick, may separate heat exchanger zones between which even very small leaks are intolerable. A large number of such joints are included in a single heat exchange and each joint must meet the same high standards of reliability.
Although roller swaging has been used to form tube/tube sheet joints, hydraulic swaging has proven to be superior. Hydraulic swaging pressures as high as 50,000 p.s.i. can be uniformly applied throughout a selected axial portion of the tube.
A hydraulic mandrel is inserted in the portion of the tube within the tube sheet, and axially separated seals carried by the mandrel define a pressure zone in which the pressure is to be applied. Pressurized fluid is then introduced through the mandrel into a small annular space between the mandrel and the tube to expand the tube radially. Typically the pressure is first generated by a pump and then multiplied by an intensifier before it is supplied to the mandrel.
A skilled worker must insert the mandrel in each tube individually and cause pressure to be applied by the operation of a control valve. Once the valve has been opened, sufficient time must be allowed for the pressure to reach the desired level. For best results, the pressure should be held at that level for a finite time period on the order of magnitude of two seconds. The optimum swaging pressure varies, depending on the specific characteristics of the tube and the tube sheet.
Ideally the swaging apparatus should be automated to the greatest extent possible to reduce the likelihood of human errors. These errors could occur if, for example, the apparatus were not properly adjusted to produce the swaging pressure desired, the operator did not wait for the system pressure to reach the desired level, or the desired swaging pressure level was not held for a sufficient time period.
A primary objective of the present invention is to provide a swaging apparatus for use in forming tube/tube sheet joints which is automated to reduce the possibility of human error. A further objective is to provide such an apparatus that is easily and simply adjustable for operation at different swaging pressures. A still further objective is the provision of such an apparatus that is highly efficient and permits each of many joints to be formed within a minimum time period.